Method for manufacturing semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device in which a source contact plug and a drain contact plug are formed. The method includes the steps of etching part of the semiconductor substrate to form a step, thus forming an overlay vernier, and forming a hard mask on the step so that the step is maintained.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Korean patent applicationnumber 10-2006-106688, filed on Oct. 31, 2006, which is incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to semiconductor devices and, moreparticularly, to a method of manufacturing a semiconductor device, inwhich an overlay vernier is formed.

In general, when fabricating semiconductor devices, a patterning processfor forming a pattern on a semiconductor substrate is performed. Inorder to perform the patterning process, a photoresist is formed on thesemiconductor substrate and then an exposure process forphotosensitizing the photoresist by irradiating light on a photomaskphoto or a reticle is performed.

A development process for removing the patterns of the photoresist thathas been photosensitized by the exposure process is performed. After thedevelopment process, an overlay vernier formed through the aboveprocesses is measured by irradiating light.

The overlay vernier is formed in order to know and correct an alignmentstate between a layer formed in a previous process (when fabricating asemiconductor device of a stack structure) and a layer formed in acurrent process. The overlay vernier is formed on the semiconductorsubstrate along with a real pattern, preferably by forming a step.

In other words, a lower overlay vernier pattern is formed along with theformation of a lower layer pattern of a real cell, and an upper overlayvernier pattern is formed along with the formation of an upper layerpattern of the real cell. The degree in which the two layers overlapwith each other is detected by using the lower overlay vernier patternand the upper overlay vernier pattern.

Meanwhile, in order to perform the exposure process, an alignmentprocess by reading an alignment key using irradiating light must beperformed. Accordingly, the alignment process can be performed only whena step, which becomes a visible marker for reading using light, isformed or an upper hard mask is made from transparent material.Furthermore, the measurement of the overlay vernier, which is performedafter the development process, also can only be performed when a step isformed or an upper hard mask is made from transparent material.

As the size of a semiconductor device is gradually miniaturized and thelevel of integration of a semiconductor device is gradually increased,however, a technique for forming a micro pattern has been developed. Inthe past, the hard mask was formed from oxide, etc. through which lightcan pass. However, recently, the hard mask has been formed fromamorphous carbon.

Amorphous carbon is an opaque material through which light cannot pass.Thus, in order to perform an alignment process performed at the time ofthe exposure process and an overlay vernier read process performed afterthe development process, an additional process for forming a step mustbe carried out.

Therefore, after a drain key open mask process and a drain key open etchprocess are performed after the deposition of an insulating layer, anamorphous carbon hard mask or the like, must be formed on the upperside. However, it increases the process steps compared to using thetransparent hard mask. Consequently, there are problems in that anoverall process time is lengthened and the cost of production isincreased.

SUMMARY OF THE INVENTION

The present invention relates to a technique capable of forming anoverlay vernier without performing additional drain key open mask anddrain key open etch processes in such a manner that a step is formed ina semiconductor substrate when the overlay vernier is formed, and a hardmask having a stack layer formed thereon is formed so that the shape ofthe step can be maintained.

According to an aspect of the present invention, there is provided amethod of manufacturing a semiconductor device in which a source contactplug and a drain contact plug are formed, including the steps of etchingpart of the semiconductor substrate to form a step, thus forming anoverlay vernier, forming a hard mask on the step so that the step ismaintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are cross-sectional views illustrating a method ofmanufacturing a semiconductor device according to an embodiment of thepresent invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

A specific embodiment according to the present patent will be describedwith reference to the accompanying drawings.

Referring to FIG. 1A, there is provided a semiconductor substrate 100including a real cell (not illustrated) in which specific patterns, suchas an isolation layer (not illustrated) and a gate (not illustrated),are formed, and a scribe line in which an overlay vernier is formed. Inthe real cell and the scribe line, processes to be described later areperformed at the same time.

An etch-stop layer 102 is formed on the semiconductor substrate 100. Theetch-stop layer 102 can include a Self-Aligned Contact (SAC) nitridelayer. Further, in order to form a source contact hole in the real cell,an etch process employing a source contact mask (not illustrated) iscarried out. In this case, the etch process is also performed in thescribe line. Thus, some of the etch-stop layer 102 and the semiconductorsubstrate 100 are removed, and a step is formed between a region fromwhich the etch-stop layer 102 and the semiconductor substrate 100 havebeen removed and a region from which the etch-stop layer 102 and thesemiconductor substrate 100 have not been removed.

In this case, the region from which the etch-stop layer 102 and thesemiconductor substrate 100 have been removed has a relatively widewidth and a relatively large pattern, compared with the cell contact.Therefore, the region can be further etched by means of a loadingphenomenon compared with the cell contact. It is therefore possible toform a sufficiently deep step.

Meanwhile, the height of the region from which the etch-stop layer 102and the semiconductor substrate 100 have been removed can be about 0.7μm, but is not limited thereto. It is evident that the height and shapeof the region from which the etch-stop layer 102 and the semiconductorsubstrate 100 have been removed can be freely changed to the extent thatthe step can be formed effectively.

Referring to FIG. 1B, in order to fill the source contact hole in thereal cell, a conductive layer 104 is formed on the entire surfaceincluding the etch-stop layer 102 and the semiconductor substrate 100.The conductive layer 104 is formed to a thickness in which the regionfrom which the etch-stop layer 102 and the semiconductor substrate 100have been removed in the above process can have a step shape withoutbeing fully filled. The conductive layer 104 can be formed frommaterial, which is conductive and can be made thin, e.g., tungsten (W).

Referring to FIG. 1C, in order to form a source contact plug in the realcell, a Chemical Mechanical Polishing (CMP) process is performed on theconductive layer 104. In this case, since a sufficiently deep step isformed due to the loading phenomenon and the CMP process is stopped inthe etch-stop layer 102, the step formed due to the removed region canbe kept intact. The step can be used as an overlay vernier, which is areference when forming the source contact plug.

Referring to FIG. 1D, in order to form an insulating layer in the realcell, an insulating layer 106 is formed on the entire surface includingthe etch-stop layer 102 and the conductive layer 104. The insulatinglayer 106 is formed so that the shape of the step is maintained.

Referring to FIG. 1E, in order to form a drain contact plug in the realcell, a hard mask 108 is formed on the insulating layer 106. The hardmask 108 can be formed from an amorphous carbon layer. The amorphouscarbon layer has a good flow physical property, and therefore can beformed to maintain the shape of the step.

When fabricating a semiconductor device of a stack structure in asubsequent process, the step can be used to know and correct analignment state between a layer formed in a previous process and a layerformed in a current process. It is therefore possible to form an overlayvernier, which becomes a reference when forming the drain contact plug.Accordingly, a drain key open mask process and a drain key open etchprocess, which are additionally performed in order to form a step in theprior art due to an opaque amorphous carbon layer, can be omitted.

According to the present invention, when a source contact is formed,some regions of a semiconductor substrate in a scribe line are etched toform a step, forming an overlay vernier for forming a source contactplug. A stack layer is formed on an upper side so that the shape of thestep can be maintained, forming a hard mask. It is therefore possible toform an overlay vernier for forming a drain contact plug withoutperforming additional drain key open mask and drain key open etchprocesses. Therefore, even when a hard mask is an opaque layer, it isnot necessary to perform an additional overlay vernier formationprocess. Accordingly, there are advantages in that the process can besimplified, process time can be shortened, manufacturing cost can besaved, and the reliability of a device can be improved.

Although the foregoing description has been made with reference to thevarious embodiments, it is to be understood that changes andmodifications of the present patent may be made by the ordinary skilledin the art without departing from the spirit and scope of the presentpatent and appended claims.

1. A method of manufacturing a semiconductor device in which a sourcecontact plug and a drain contact plug are formed, the method comprising:etching part of the semiconductor substrate to form a step in order toform an overlay vernier; and forming a hard mask on the step to protectthe step.
 2. The method of claim 1, wherein the hard mask is formed froman opaque material through which light cannot pass.
 3. The method ofclaim 2, wherein the hard mask includes an amorphous carbon layer. 4.The method of claim 1, wherein the step is used as an overlay vernierwhen a source contact plug and a drain contact plug are formed.